Process for making abrasive article



March 12, 1957 G. F. KEELERIC 2,785,060

PROCESS FOR MAKING ABRASIVE ARTICLE Filed Oct. 15, 1952 Unite PROCESS FQR MAKING ABRASIVE ARTICLE George F. Keeleric, Dundee, Ill.

Application October 15, 1952, Serial No. 314,881

8 Claims. (Cl. 51-369) This invention relates to the distribution of particles in a single layer over a surface and particularly to the distribution of abrasive particles to form a grinding face.

In the manufacture of abrasive tools it is sometimes desirable to use a single layer of abrasive particles to form the grinding face. Particularly where diamond cart or other costly materials are used this is important although there are other factors besides cost which make a single layer abrasive tool desirable. When such tools, e. g. grinding wheels, are to be made, the abrasive particles are fastened in one way or another to a solid material such as metal or plastic. My Patent, No. 2,368,473, issued lune 30, 194-5, for Method of Making Abrasive Articles discloses one method for making such single layer abrasive tools.

It is desirable in such a single layer abrasive tool that the abrasive particles be spaced somewhat one from another in order to achieve effective abrasive action. If the particles touch one another, the cutting action is impaired. But it has been very difficult to achieve uniform spacing or distribution of the particles; there is a tendency for the particles to cluster closely together over a part of the surface of the tool and to be spread too far apart elsewhere.

But when uniform spacing and controlled density of coverage is obtained a much improved cutting action follows-and a considerable economy in materials used is obtained.

To distribute the thousands of small particles manually would be out of the question commercially. Electrostatic application of the particles may be of some assistonce but in a single layer tool this technique is ditiicnlt to control in such a way as to bring about a controlled degree of coverage. And when diamond particles are used, the electrostatic process is more dilhcult because of the generally non-conductive property of diamonds and because of unavoidable variations in this respect and others of one particle from another.

ere it should be pointed out that it is desirable not only that spacing between the particles be reasonably uniform but also that it be controlled so as to achieve determinate coverage of the base surface. Thus, for some grinding applications 25% of the base surface should be covered by abrasive particles While in others 50% or more should be covered. Methodssuch as the electrostatic method may at best provide uniform spacing but cannot provide, in a single layer abrasive tool, requisite control of coverage because of the number of hard to control variables such as velocity of particles, density, bouncing, and time of exposure. These factors are of less importance in multiple layer applications or even in single layer applications where practically 100% coverage is intended or even where the degree of coverage need not be accurately controlled.

Accordingly, it is the object of my invention to achieve reasonably uniform distribution of abrasive particles over a base material and to achieve close control of the degree of coverage of the base material by the particles. And it 2,785,060 Patented Mar. 12, 1957 is part of my object to achieve such results in an economical manner suitable for production application.

The way I accomplish my object will best be understood by reference to the drawings and description which follows.

In the drawings:

Fig. l is a plan view showing abrasive particles and other particles in position at an early stage in manufacture.

Fig. 2 is a sectional view of Fig. 1.

Fig. 3 is the same view as Fig. 1 at a later stage showing the abrasive particles in position.

All views show only a portion of the total abrasive tool surface and Figures 1 and 2 are taken from actual microscopic photographs. The approximate scale can be determined from the size of the abrasive particles which, in this case, had an actual average maximum dimension of the order of .004 inch.

In the preferred practice of my invention, the teci niques disclosed in my above identified patent (No. 2,368,473 of June 30, 1945) will be used although they are not essential to this invention.

The crux of my invention resides in mixing the abrasive particles with a soluble or otherwise removable material prior to application to the base material.

Referring to the drawings, 1 provide a blank or form 13. (This blank ultimately forms no part of the abrasive tool, serving only as a mounting surface to obtain uniform height of the particles. The finished abrasive surfaces of the particles are those which initially are in contact with the blank or form 18.) On the blank 18 is spread a very thin coating of adhesive 19. to be scarcely visible. The adhesive, as disclosed in my above-identified patent (No. 2,368,473 of lune30, 1945) may be of a type characterized by a tacky quality when first applied and susceptible of hardening or setting thereafter either with or without the application of heat.

Now, to spread the abrasive particles 15 over the adhesive 19 with uniform spacing in a controlleddegree, I first make a mixture of the abrasive particles and some other particles 15a which are water soluble, and then scatter this mixture over the blank or form 18 until the entire surface is covered with the mixture (subject of course to inevitable interstices) so that all of the particles which make contact with the adhesive are held in place by it. 7

The making of the mixture of particles, abrasive and others, is of controlling importance. With diamond powder I first screen the diamond powder to the desired grit size, for example, 100 mesh. Then I take rock salt (sodium chloride) and crush it and then screen it to ice approximately the same grit size as the diamond powder;

Where a high percentage of coverage or density is desired, better distribution will be obtained by grinding and screen ing the salt to a finer grit size. The two powders, diamond and salt, are then thoroughly mixed in the desired proportions. The proportionof diamond dust to salt determines the extent of ultimate abrasive coverage of the surface.

Thus for grinding wheels to be used in ordinary grinding of'carbide tools, I have found 25% coverage desirable. Accordingly, the mixture of diamond dust and salt is made in the proportion of 25% diamond dust and salt by volume.

For electrolytic grinding or shaping as disclosed in my co-pendiug application, Serial No. 319,244 filed September 18, 1952, for Method and Apparatus for Electrolytic Cutting, Shaping and Grinding, I prefer to use about 50% Thorough mixing is important. To know that good mixing has been achieved it is desirable to color the salt which may be done by first making a saturated solution This coating is so thin as thoroughness of the mixing. can be checked by the uni formity of the color.

The mixture may be applied by a sitter to the adhesive 19 and no care need be taken to avoid an excess as only the particles which touch the adhesive will adhere to it and the excess may be eliminated by tilting the blank or form 18. The mixture which falls off may be recaptured and used again.

When the adhesive has hardened, the form 18 carrying all of the particles, diamond and salt, is immersed in water until the salt particles 15a are entirely dissolved. The form may then be rinsed in fresh water to eliminate the last salt traces. The adhesive used should, of course, not be soluble in water. At this point the blank or form 18 will appear as in Fig. 3 with the diamond particles 15 more or less evenly spaced one from another entirely at random and with a density proportional to the initial mixture. As shown in Fig. 3 the density is approximately 30%; that is, there are 30% as many diamond particles as there would be if the maximum number the form would hold had been attached.

I have successfully made grinding wheels varying in density of particles from to 75% by making the initial mixtures in these proportions. When high densities are desired with uniform spacing, it is desirable that the removable salt particles be crushed and screened to a much finer grit size than the diamond dust before mixing.

Once the abrasive particles have been fastened to I the form 18, the process of making the backing for the tool is carried out as described in my aforementioned patent. Since this process is fully disclosed in my aforementioned patent, it is not necessary to set it forth fully here. Briefly, a thin plating of metal such as copper is applied to the form 18 on top of the adhesive 19. Then a heavier layer of metal such as nickel or iron is plated on to a thickness sulficient to hold the particles firmly. This layer is then trued off to a flat surface and fastened as by soldering to a heavy permanent mounting wheel. When these steps have been carried out, the blank or form 18 is pulled away exposing the downward ends of particles 15. Then the copper is etched away and the particles protrude from the grinding wheel by the thickness of the removed copper. Thus I am able to control the spacing of the particles, the density of their application and the extent of their protrusion.

Naturally, materials other than abrasives may be used where the purpose is not to make grinding tools. Thus luminescent particles may be applied in this manner. Also it is not necessary to use salt as the material for the removable particles 15a. But the material should not be sticky and should mix easily and should be easily selectively removable by dissolution or by evaporation or by sublimation. In special cases crushed ice may be used to make the removable particles. In such case the mixing and application of particles must be carried out at reduced temperature. The same may be done with Dry Ice (CO2) as the removable particles. To remove such particles the temperature is raised and the ice melts and flows away. Dry Ice sublimates directly to a gas.

By the broad range of permanent and removable particles available, the process may be applied in a wide l. The process of making an abrasive article which includes the steps of placing a very thin layer of tacky,

water-insoluble adhesive on a form, placing a thorough mixture of well mixed diamond powder and water-soluble salt powder on the tacky adhesive so that a layer of the mixture adheres thereto, then dissolving away the salt, then depositing a metallic bond around the remaining particles of diamond powder, and then removing the form from the diamond powder and the bond.

2. The process of making an abrasive article having a determinate proportion of its working surface covered by abrasive particles which includes the steps of placing a very thin layer of tacky, water-insoluble adhesive on a form, placing a thorough mixture of well mixed diamond powder and water-soluble salt powder in the proportion of diamond powder to salt powder which is desired as the proportionate determinate coverage of the working surface by abrasive particles on the tacky adhesive so that a layer of the mixture adheres thereto, then dissolving away the salt, then depositing a metallic bond around the remaining particles of diamond powder, and then removing the form from the diamond powder and the bond.

3. The process of making an abrasive article which includes the steps of placing a very thin layer of tacky, water-insoluble adhesive on a form, placing a thorough mixture of well-mixed, water-insoluble abrasive powder and water-soluble salt powder on the tacky adhesive so that a layer of the mixture adheres thereto, then dissolving away the salt, then depositing a metallic bond around the remaining particles of water-insoluble abrasive powder, and then removing the form from the waterinsoluble abrasive powder and the bond.

4. The process as defined in claim 3 in which the abrasive powder is of a color different from the watersoluble salt powder and in which the two powders are mixed before application until a uniform color is visible throughout the mixture.

5. The process of making an abrasive article having a determinate proportion of its working surface covered by abrasive particles which includes the steps of placing a very thin layer of tacky, water-insoluble adhesive on a form, placing a thorough mixture of well-mixed, waterinsoluble abrasive powder and water-soluble salt powder in the proportion of water-insoluble abrasive powder to salt powder which is desired as the proportionate determinate coverage of the working surface by abrasive particles on the tacky adhesive so that a layer of the mixture adheres thereto, then dissolving away the salt, then depositing a metallic bond around the remaining particles of water-insoluble abrasive powder, and then removing theform from the water-insoluble abrasive powder and the bond.

6. The process of making an abrasive article which includes the steps of placing a very thin layer of tacky, water-insoluble adhesive on a form, placing a thorough mixture of well-mixed diamond powder and water-soluble salt powder on the tacky adhesive so that a layer of the mixture adheres thereto, then dissolving away the salt, then depositing a bond around the remaining particles of diamond powder, and then removing the form from the diamond powder and the bond.

7. The process of making an abrasive article which includes the steps Ofplacing a very thin layer of tacky, water-insoluble adhesive on a form, placing a thorough mixture of well-mixed, water-insoluble abrasive powder and water-soluble salt powder on the tacky adhesive so that a layer of the mixture adheres thereto, then dissolving away the salt, then depositing a bond around the remainingparticles of water-insoluble abrasive powder, and then removing the form from the water-insoluble abrasive powder and the bond.

8. The process of making an abrasive article having a determinate proportion of its working surface covered by abrasive particles which includes the steps of placing 5 a very thin layer of tacky, water-insoluble adhesive on a form, placing a thorough mixture of well-mixed, waterinsoluble abrasive powder and Water-soluble salt powder in the proportion of water-insoluble abrasive powder to salt powder which is desired as the proportionate determinate coverage of the working surface by abrasive particles on the tacky adhesive so that a layer of the mixture adheres thereto, then dissolving away the salt, then depositing a bond around the remaining particles of waterinsoluble abrasive powder, and then removing the form 10 from the water-insoluble abrasive powder and the bond.

References Cited in the file of this patent UNITED STATES PATENTS Ford May 25, 1886 Johnston Sept. 5, 1893 Snyder Ian. 22, 1907 Lowrey Mar. 30, 1915 Keeleric Jan. 30, 1945 Nadeau Oct. 9, 1945 Glaser et al May 22, 1951 Simons Oct. 16, 1951 

1. THE PROCESS OF MAKING AN ABRASIVE ARTICLE WHICH INCLUDES THE STEPS OF PLACING A VERY THIN LAYER OF TACKY, WATER-INSOLUBLE ADHESIVE ON A FORM, PLACING A THROUGH MIXTURE OF WELL MIXED DIAMOND POWDER AND WATER-SOLUBLE SALT POWDER ON THE TACKY ADHESIVE SO THAT A LAYER OF THE MIXTURE ADHERES THERETO, THEN DISSOLVING AWAY THE SALT, THEN DEPOSITING A METALLIC BOND AROUNBD THE REMAINING PARRTICLES OF DIAMOND POWDER, AND THEN REMOVING THE FORM FROM THE DIAMOND POWDER AND THE BOND. 